Groundwater is a last-resort source of domestic water supply in Dar es Salaam City because of the scarcity of surface water sources. The Tanzania Government, Non Government Organizations (NGOs), Community Based Organizations (CBOs) and international aid organizations have promoted the drilling of boreholes. From 1997 until the present, boreholes drilling has increased tremendously and the trend is expected to increase even more in the future. Initial assessment of the current state of water quality indicates that the coastal aquifers are vulnerable to saline intrusion. In some areas, overpumping of the groundwater has resulted in encroachment of sea water into the coastal aquifers. Water samples from Mikocheni, Oysterbay, Msasani, Masaki and City Centre areas show elevated chloride, sulphate and sodium concentrations. Using Stuyfzand (1986) water classification method, over 50 percent of the samples showed the type of fresh-brackish to salt and extremely hard. Residents depend on the shallow aquifer at less than 15 m, because at this depth the water is relatively less saline. The saltwater interface is likely to be moving inland on seasonal basis and some boreholes become more saline in late summer. The growing human population in and around the investigated areas has had an adverse impact on the water in the shallow aquifer through, among other factors, indiscriminate abstraction of water without knowledge of the aquifer's capacity. In order to prevent further deterioration of the aquifer, there is a need to establish an inventory of the wells, conduct proper pump tests and geochemical characterization to ascertain the capacity of the shallow aquifer and understand the processes affecting the overall quality of the groundwater.